1. Field of the Invention
The present invention relates to energy systems for powering elevators, in particularly an energy system utilizing a primary and an auxiliary motor for reducing the required power of the system.
2. Description of Related Art
Elevators are a standard fixture of practically every multi-story edifice on the globe. Elevators not only provide access to disabled of otherwise inaccessible areas but provide a modem convenience to those who work and live in buildings having more than one floor. Since the inception of the elevator, a simple method has been used to power the system which is reliable and safe, and provides the greatest convenience to the user. Most elevators operate by means of a tried and true system whereby a large DC (direct current) motor is used to lift a cabin suspended by cables. The DC elevator motor is necessarily large in order to generate the great power required to lift the cabin from a stand still with its maximum load capacity, further accounting for overloads and factors of safety. While such a motor could be operated directly from the AC (alternating current) source supplied directly from the power company, for several reasons it is more efficient to have a localized direct current supply available from which to draw the current needed for the elevator motor. First, there is a large surge in the current when such a motor is started resulting a spike, which is dangerous to the system and its components. The spike also results in a peak current, which in most areas determines the supplier's rate at which a designated period of usage costs the user. That is, if the pre-set interval that the power company charges a customer is four hours, the large spike at the ignition of the DC motor during the four hour period sets the rate for the entire period (even if the spike lasts only a few seconds). For this reason, most systems employ a DC generator which provides a ready source of DC current for the DC motor which operates the elevator.
The presence of the DC generator solves the problem of a spike occurring when the elevator motor is started, but the generator itself requires a source of power. Typical systems employ a large AC motor to run the DC generator, and usually this combination is sold as a single motor/generator unit. With the AC motor running continuously, the generator provides a constant source of power to the elevator motor eliminating all but the most minor spikes in the current draw. However, the problem lies in the continuous running of large AC motor. A large AC motor running under a no load condition, i.e., with the elevator motor not drawing power from the generator, will still require a current of up to 40% of the maximum load current. When this current is projected over a twenty four hour period, as many elevators require, and then over a 365 day year, the cost of simple powering the elevator is staggering. This is true especially when one considers that the elevator is actually being used in the neighborhood of 20 percent of the time during peak hours.
To date, the inventor knows of no solution which has been attempted to reduce the power in elevator systems while meeting the safety requirements and operational parameters of existing elevator systems. A solution should ideally be adapted for use with existing systems with little modification, and should be applicable to different sizes and capacity elevators.